Pontiff to Visit Slum With Local Priest as Church Seeks to Emphasize Need to Reach Out to Destitute

RIO DE JANEIRO—In the teeming slums that cling to the cliffs above Rio de Janeiro, Father Luiz Antônio Pereira Lopes says he wages an often lonely struggle to keep Catholicism alive amid a rapid expansion of Evangelical Protestantism among the poor in recent decades.

The self-built communities of tin-roof shacks where he preaches are the product of a chaotic period of urbanization, and were long neglected by institutions from the police and hospitals, to the Catholic Church. Evangelical pastors found fertile ground in...